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Studies  in  the  Adsorption  of 
Charcoal 


A  DISSERTATION 

PRESENTED  TO  THE  FACULTY  OF  PRINCETON  UNIVERSITY  IN 

CANDIDACY  FOR  THE  DEGREE  OF  DOCTOR 

OF  PHILOSOPHY 


BY 

HOMER  HIRAM  LOWRY 


EASTON,  PA.: 
ESCHENBACH  PRINTING  COMPANY 

I92O 


ACCEPTED  BY  THE  DEPARTMENT  OP  CHEMISTRY 
JUNE,  1920 


0071? 


Q.C 


STUDIES  IN  THE  ADSORPTION  BY  CHARCOAL. 
I.  THE  RELATION  OF  SERVICE  TIME  TO  ADSORPTION  AND  ABSORPTION. 


Introduction. 

Because  of  the  prominence  of  gas  warfare  in  the  recent  world  war, 
means  of  protection  against  gas  had  to  be  developed.  Naturally  char- 
coal played  a  prominent  part  because  of  its  remarkable  properties  as  an 
absorbent.  Also  naturally  one  sample  of  charcoal  prepared  in  one  way 
might  be  better  than  another  for  a  given  use  and  the  test  developed  to 
show  superiority  of  one  charcoal  over  another  became  known  as  the  "ser- 
vice time"  test.  This  method  of  testing  has  been  described  by  Lamb, 
Wilson,  and  Chancy1  and  was  purely  an  empirical  test  developed  to  ap- 
proximate field  conditions.  Briefly,  it  consisted  in  passing  air  contain- 
ing a  known  concentration  of  a  toxic  gas,  as  chloropicrin,  at  a  definite 
rate  through  a  sample  of  charcoal  of  standard  dimensions  until  the  gas 
could  be  detected  in  the  effluent  air.'  The  test  gave  the  desired  data  but 
had  no  theoretical  basis,  though  many  speculations  had  been  made  on 
this  point.  No  known  property  of  a  charcoal  could,  however,  lead  one 
to  say  that  it  would  give  a  better  test  than  another  without  actually  sub- 
mitting it  to  these  empirical  conditions. 

The  lack  of  relation  between  service  time  and  some  physical  proper- 
ties of  various  charcoals  is  shown  in  Table  I. 
1  J.  Ind.  Eng.  Chem.,  n,  430  (1919). 


189499 


TABLE  I.1 

A909.  Nela.  English.  German. 

Density: 

True 1.84  1.89  1.86  1.70 

Apparent 0.55  0.46  0.13  0.24 

Vol.  capillaries  per  cc 0.23  0.31  0.39  0.38 

Service  Time: 

Cal.  minutes  (accelerated) 17.3  53.5  8.8  60. 2° 

%wt.  C(NO2)C13  at  break  point 14.6  48.7  32.0  110.0° 

a  This  value  was  obtained  not  on  the  charcoal  as  taken  from  the  canisters  but  after 

having  been  treated  as  described  later. 

Most  of  the  speculations  on  service  time  have  connected  this  property 
with  either  the  well  known  great  adsorptive  power  of  charcoal  or  with 
capillary  action  due  to  its  porous  structure.  We  wished  to  investigate 
this  relation  and  decided  to  measure  the  adsorptive  power  of  these  char- 
coals for  nitrogen,  carbon  dioxide  and  water  vapor.  These  were  chosen 
because  they  were  well  defined,  stable  substances  not  very  difficult  of 
preparation  in  the  pure  state,  and  were  widely  different  as  to  critical 
temperatures.  Attention  is  called  to  this  fact  that  at  25°,  the  tempera- 
ture chosen  for  the  measurements,  water  is  normally  a  liquid,  carbon  di- 
oxide is  a  gas  just  below  its  critical  temperature,  and  nitrogen  a  gas  and 
far  above  its  critical  temperature. 

It  was  also  realized  that  we  had  an  opportunity  to  obtain  adsorption 
measurements  on  charcoals  which  had  been  prepared  in  a  very  definite 
way  and  their  other  characteristics  determined  in  the  work  on  the  various 
charcoals  used  for  gas  masks.  Previous  measurements,  as  given  in  the 
literature,  may  be  considered  to  have  doubtful  value  because  of  their 
non-reproducibility,  since  no  special  attention  was  given  to  the  prepara- 
tion of  the  charcoal,  to  activation,  and  to  the  other  physical  properties 
of  the  charcoal.  Only  in  this  sense  was  it  intended  to  supplement  the 

1  NOTE. — The  method  of  determination  of  these  properties  follows: 

True  Density. — Charcoal  placed  in  sample  tube  and  evacuated  at  445°  and  sealed 
in  vacuo.  Weighed  in  air,  then  opened  under  water  and,  after  the  "drift"  had  disap- 
peared, the  weight  determined,  and  volume  obtained  from  weight  of  water  displaced 
(THIS  JOURNAL,  42,  391  (1920)). 

Apparent  Density. — These  figures  are  calculated  on  a  moisture-  and  gas-free  basis. 

Volume  of  Capillaries. — Values  obtained  by  centrifuging  the  sample  of  charcoal 
opened  under  water  in  the  density  determination  for  a  definite  period  of  time  and 
approximately  1000  r.  p.  m.  The  excess  weight  of  the  sample  over  the  true  weight  of 
the  charcoal  represented  the  water  retained  by  the  capillaries  and  is  essentially  the 
same  as  if  the  external  water  were  removed  by  filter  paper. 

Service  Time. — These  tests  were  made  by  Dr.  N.  K.  Chancy,  of  the  National  Carbon 
Co.,  by  the  standard  accelerated  method  except  that  the  rate  was  500  cc.  per  minute 
instead  of  the  usual  1000  cc.,  i.  e.,  the  test  is  only  half  as  accelerated  as  the  standard. 
From  the  actual  weight  of  the  chloropicrin  absorbed,  the  minutes  service  was  calculated. 
We  wish  to  express  here  our  sincere  thanks  to  Dr.  Chancy  for  furnishing  us  with  this 
data. 


enormous  amounts  of  data  already  collected  on  the  adsorption  of  gases  by 
charcoal.  Special  interest,  however,  was  attached  to  the  adsorption  of 
water  vapor,  first  because  no  accurate  measurements  of  the  adsorption 
of  vapors  by  charcoal,  which  could  normally  exist  as  liquids  at  the  tem- 
perature of  the  measurements,  have  previously  been  recorded  in  the  litera- 
ture, and  secondly,  because  the  so-called  toxic  "gases"  of  warfare  were 
usually  such  vapors. 

Description  of  the  Charcoals. 

Agog. — This  charcoal  was  prepared  at  Astoria  in  August,  1918,  from 
cocoanut  shells.  The  preliminary  carbonization  was  at  950°  for  10  hours. 
The  sample  was  then  steam-activated  at  950°  for  45  minutes  according  to 
a  method  described  in  detail  elsewhere.1  The  sample  used  was  18-20 
mesh,  i.  e.,  that  which  would  pass  through  an  i8-mesh  screen  but  was 
retained  by  a  2o-mesh  screen. 

Agog  Es. — This  was  the  same  charcoal  as  the  preceding,  the  only 
difference  being  in  the  size  of  the  particles.  It  was  prepared  by  grinding 
the  coarse  Agog  in  a  ball  mill  and  collecting  by  electrical  precipitation 
the  dust  which  was  too  fine  to  settle.2  The  maximum  diameter  of  the 
particles  as  determined  microscopically  was  one  micron,  o.ooi  mm. 

Nela. — This  was  a  mixture  of  cocoanut  charcoals  prepared  and 
activated  in  the  C.  W.  S.  Laboratory  at  Nela  Park,  Cleveland.  The  char- 
coals composing  this  mixture  were  very  similar  but  of  various  degrees  of 
activity.  The  preliminary  carbonization  was  made  at  950°  for  10  hours 
and  the  charcoals  were  then  activated  with  steam  at  950°  for  approxi- 
mately 45  minutes. 

English. — This  was  a  mixture  of  English  charcoals  which  were  very 
similar.  These  charcoals  were  made  from  birch  wood  in  gas  retorts,  that 
is,  they  were  really  air  activated.  The  method  of  preparation  was  the 
standard  adopted  for  the  preparation  of  British  war  charcoals. 

German. — For  the  details  of  the  method  of  preparation  of  this  char- 
coal, the  reader  is  referred  to  an  article  by  J.  F.  Norris.3     Briefly,  the  car- 
bonization was  affected  as  follows.     The  wood  in  pieces  of  uniform  size 
was  soaked  in  a  hydrochloric  acid  solution  of  zinc  chloride  for  about  l/z 
hour.     The  acidified  wood  was  then  heated  in  a  closed  muffle  furnace 
at  a  cherry-red  for  at  least  6  to  8  hours.     The  charcoal  obtained  was 
washed  with  hydrochloric  acid  until  the  soluble  ash  was  reduced  to  a 
minimum.     The  finished  product  contained  about  0.01%  of  zinc.     It 
was  finally  washed  free  from  acid,  drained  on  a  grill,  and  dried  in  a  vacuum 
at  70°  to  80°.     This  sample  of  charcoal  was  taken  from  unused  canisters 
which  had  been  captured  in  September,  1918,  and  was  further  treated 
1  J.  Ind.  Eng.  Chem.,  II,  430  (1919). 
-  J.  Am.  Chem.  Soc.,  42,391  (1920). 
3  Norris,  /.  Ind.  Eng.  Chem.,  n,  829  (1919). 


before  using  it  in  the  measurements,  including  those  of  the  service  time, 
as  follows.  It  was  boiled  in  distilled  water  for  2  hours,  its  water  decanted 
and  this  treatment  repeated  7  times.  It  was  then  boiled  for  3  hours  in 
dil.  (i  :  7)  hydrochloric  acid,  the  acid  decanted  and  then  again  treated 
as  at  first  3  times  with  water.  It  was  dried  in  the  air  on  filter  paper, 
and  then  for  5  hours  at  110-115°  in  aif  free  from  carbon  dioxide  and 
water  vapor. 

Preparation  of  Nitrogen,  Carbon  Dioxide,  and  Water. 
Nitrogen. — A  mixture  of  air  with  hydrogen  from  a  Kipp  generator 
using  dil.  hydrochloric  acid  and  zinc  metal,  was  forced  through  a  combus- 
tion tube  in  the  proper  proportions  to  remove  completely  the  oxygen  and 
hydrogen,  using  copper-copper  oxide  as  the  indicator.1  The  effluent  gases, 
nitrogen  and  argon,  were  collected  and  stored  in  a  large  glass  gasometer 
over  a  dil.  alkaline  pyrogallate  solution  in  order  that  they  might  not  be 
contaminated  with  the  oxygen  originally  dissolved  in  the  water.  Subse- 
quent analysis  showed  no  traces  of  oxygen,  carbon  monoxide,  carbon 
dioxide,  or  hydrogen,  Assuming  that  the  air  originally  contained  78% 
of  nitrogen  and  i%  of  argon,  the  "nitrogen"  used  contained  1.25% 
argon.  The  gas,  as  used,  was  dried  by  passage  over  calcium  chloride 
and  phosphorus  pentoxide. 

Carbon  Dioxide. — The  carbon   dioxide   was   prepared   by   dropping 
i  :  i  sulfuric  acid,  kept  in  an  atmosphere  of  carbon  dioxide,  on  a  saturated 

solution  of  sodium  hydrogen  carbonate. 
The  sulfuric  acid  had  been  previously 
saturated  with  carbon  dioxide  to  dis- 
place the  dissolved  gases.  The  gas  was 
dried  over  calcium  chloride  and  phos- 
phorus pentoxide.  Analysis  showed  a 
residue  of  less  than  0.1%  of  gas  not 
absorbed  by  a  caustic  potash  solution. 
The  gas  was  generated  as  used. 

Water. — The  water  used  was  ordi- 
nary distilled  water  freed  from  dissolved 
gases  as  follows.  About  10  cc.  of  dis- 
tilled water  was  placed  in  the  tube  T, 
j-p  Fig.  i,  and  the  system  partially  evac- 
uated  through  the  stopcock  M  by 
means  of  a  Topler  pump.  The  water 
was  then  carefully  frozen  with  solid  car- 
bon dioxide  and  ether  and  the  system 
evacuated  to  the  vapor  pressure  of  water 
at  that  temperature.  After  closing  the 
1  /.  Am.  Cliem.  Soc.,  27,  1415  (1905). 


To  Sample 

Fig.  i. 


To  Inlet  Char 


stopcock  M,  the  ice  was  allowed  to  melt  and  M  opened  again  momentarily. 
Any  air  dissolved  in  the  water  would  be  given  up  to  the  vacuum.  To  re- 
move this  air,  which  was  always  less  than  0.02  cc.,  the  water  was  again 
frozen  and  the  system  re-evacuated. 

Description  of  Apparatus. 

A  diagram  of  the  apparatus  is  shown  in  Fig.  2.  This  consisted  of  a 
quartz  tube,  NP,  15  mm.  inside  diameter,  and  about  25  cm.  in  length. 
The  sample  of  charcoal  was  placed  in  the  lower  8  to  10  cm.  of  the  tube 
and  above  this,  in  order  to  reduce  the  amount  JQ  Pump 

of  dead  space  as  much  as  possible,  there  was 
placed  another  quartz  Tube,  O,  sealed  at  both 
ends  and  fitting  tightly  in  NP.  A  ground 
glass,  vacuum-tight  joint  at  N  joined  the 
quartz  tube  containing  the  sample  to  a  3 -way 
Stopcock,  M.  By  means  of  this  stopcock,  the 
charcoal  could  be  directly  opened  to  the  reser- 
voir holding  the  gas  to  be  absorbed  or  to  a 
manometer  S  and  through  the  stopcock  R  to  a 
Topler  mercury  pump,  by  which  the  evacua- 
tion of  the  system  was  effected.  Pressures 
from  a  fraction  of  a  millimeter  to  400  mm. 
could  be  read  from  the  manometer  by  means 
of  a  cathetometer  and  a  scale  placed  between 
the  2  arms  of  the  manometer.  The  pressure 

was  read  to  the  nearest  o.i  mm.     The  volume  5 

of  the  apparatus  enclosed  by  the  stopcock  R 
and  the  quartz  tube  NP  was  measured  directly 
by  putting  the  quartz  tube  and  filler,  O,  in 
place  empty,  with  R  closed  and  the  system 
evacuated  to  R,  and  subsequent  opening  of  R 
and  evacuation  of  the  rest  of  the  apparatus, 
the  gas  being  collected  at  the  delivery  of  the 
pump  and  measured  in  a  gas  buret  to  the 
nearest  o.oi  cc.  Since  the  inside  diameter  of 
the  manometer  was  previously  measured  and 
was  of  uniform  bore,  the  volume  of  the  ap- 
paratus at  o  mm.  pressure  could  be  calculated, 
as  also  the  increase  in  volume  with  each  millimeter  pressure.  For  deter- 
mining the  free  space  in  the  apparatus  when  the  charcoal  was  in  place, 
the  volume  of  the  charcoal,  calculated  from  the  weight  of  the  gas- 
and  moisture-free  sample  and  its  previously  determined  true  density,  was 
subtracted  from  these  values. 


Fig.  2. 


Method. 

In  practice,  a  sample  of  charcoal,  containing  an  unknown  weight  of  gas 
and  moisture,  was  weighed  directly  into  the  quartz  tube  NP.  The  weight 
of  the  sample  used  depended  on  the  apparent  density  of  the  charcoal 
since  the  volume  of  the  charcoal  used  was  a  constant — about  14  cc.  In 
the  line  between  the  pump  and  the  stopcock  R  was  sealed  a  small  glass 
* — Ok  (r^  condenser  (Fig.  2  a),  which  was  immersed  in  solid  carbon  di- 
oxide and  ether  after  the  system  had  been  completely  evac- 
uated to  the  stopcock  M.  This  stopcock  was  then  opened 
and  simultaneously  an  electric  heater  was  placed  around  the 
quartz  tube,  the  ground  glass  connection  at  N  being  cooled 
by  a  lead  coil  through  which  cold  water  was  passing. 
The  heater  had  been  calibrated  and  sufficient  current  was 
passed  through  to  raise  the  sample  of  charcoal  to  750°  and 
Fig.  2a.  ft^s  temperature  was  maintained  until,  with  continual 
evacuation  by  means  of  the  Topler  pump,  less  than  o .  i  cc.  was  given 
off  in  each  lo-minute  interval.  This  condition  was  usually  obtained 
only  after  5  to  7  hours  heating.  Previous  experience  had  shown 
that  until  such  a  temperature  had  been  reached  the  effluent  gases 
contained  fairly  large  percentages  of  the  oxides  of  carbon.  The  gas 
as  given  off  was  collected  at  the  delivery  of  the  pump  and  stored  in 
a  large  gas  buret  over  mercury,  in  which  the  total  volume  of  gas  was 
measured.  An  analysis  of  a  sample  of  this  allowed  easy  calculation  of 
the  weight  of  gas  given  up  by  the  charcoal  during  the  treatment  This 
varied  with  the  charcoals  used  from  i%  to  10%  of  the  original  weight 
of  the  charcoal.  The  moisture  in  the  charcoal,  having  been  retained  in 
the  condenser  by  freezing,  was  determined  directly  by  cutting  the  con- 
denser out  of  the  line,  the  stopcock  R  being  closed,  and  weighing  the  con- 
denser with  the  water  and  then  empty.  This  moisture  varied  from  i% 
to  13%  of  the  original  weight  of  the  charcoal.  After  the  quartz  tube 
had  cooled,  it  was  kept  immersed  in  a  thermostat  at  25°  ±  0.2°,  while 
the  pressure  concentration  measurements  were  being  made.  Fairly 
close  adjustment  of  the  temperature  was  necessary  because  of  the  large 
though  undetermined  temperature  coefficient  of  pressure  with  tempera- 
ture. After  the  measurements  with  one  gas  were  obtained,  the  charcoal 
was  re-evacuated  at  184°  (aniline  b.  p.)  to  remove  the  last  traces  of  the 
adsorbed  gas. 

Admission  of  Nitrogen  and  Carbon  Dioxide. 

Since  both  these  substances  are  gases,  their  pressures  and  concentra- 
tions were  measured  similarly,  though  necessarily  differently  from  the 
method  followed  with  water,  a  description  of  which  will  be  given  later. 

For  the  admission  of  nitrogen,  the  apparatus  shown  in  Fig.  3  was  sealed 
to  the  stopcock  M  (Fig.  2).  This  apparatus  consisted  essentially  of  a 


small  gasometer,  R,  of  known  volume,  kept  immersed  in  a  jacket  of  water 
NP,  the  temperature  of  which  was  recorded  by  the  thermometer,  T.  The 
rest  of  the  apparatus  was  the  large  gasometer  in  which  the  nitrogen  was 
stored,  and  drying  tubes  containing  calcium  chloride  and  phosphorus  pent- 
oxide.  By  opening  the  stopcock,  M,  this  apparatus,  including  the  small 
gasometer  R,  could  be  completely  evacuated  to  J.  The  line  was  then 
"washed  out"  several  times  with  nitrogen  from  the  large  gasometer.  When 
this  was  accomplished,  the  small  gasometer  was  opened  to  the  nitrogen  sup- 
ply and  simultaneously  the  line  to  the  gasometer  from  the  pump  closed 


H       -I 


To  Char- 


To  Pump 


Fig.  3- 

by  turning  the  3-way  stopcock  K.  The  stopcock  J  being  opened,  the  gasom- 
eter R  was  filled  with  nitrogen  to  the  zero  mark  at  atmospheric  pressure 
by  means  of  the  leveling  bulb  L.  The  temperature  and  pressure  of  this 
volume  being  known,  it  was  readily  reduced  to  N.  T.  P.  The  volume  of 
the  gasometer  was  94 . 62  cc.  Now  the  stopcocks  K  and  M  were  so  turned 
as  to  connect  the  sample  of  charcoal  with  the  nitrogen  in  the  gasometer 
and  the  levels  of  mercury  in  L  and  R  kept  approximately  level  while  the 
gas  was  being  adsorbed.  Equlibrium  was  very  rapidly  reached  and  the 
2  levels  carefully  adjusted.  The  stopcock  M  was  then  turned  so  the  line 


between  K  and  M  and  the  gasometer  R  could  be  evacuated.  In  this  way 
the  excess  of  gas  remaining  in  the  gasometer  could  be  measured  by  col- 
lecting it  as  pumped  off  at  the  delivery  of  the  Topler  pump  and  its  vol- 
ume determined  in  a  gas  buret.  By  subtracting  this  volume,  corrected 
to  N.  T.  P.,  the  amount  of  nitrogen  in  the  quartz  tube  NP,  Fig.  2,  was 
known,  and  by  subtracting  from  this  value  the  nitrogen  in  the  previously 
determined  free  space  of  the  tube,  also  corrected  to  N.  T.  P.,  the  amount 
of  nitrogen  in  cc.  N.  T.  P.  adsorbed  at  25°  and  atmospheric  pressure  was 
760 


4      5      6      7      8      9     10    ii 
Cc.  nitrogen  per  gram. 


12    13     14 


Fig.  4. — Adsorption  isotherms  for  nitrogen  on  charcoals  at  25°. 

determined.  By  a  series  of  evacuations,  and  collecting  and  measuring 
each  volume  of  gas  as  pumped  off,  and  subtracting  this  from  the  previous 
volume  of  gas  in  the  system,  the  amount  of  nitrogen  in  the  system  at 
several  pressures  could  be  measured.  Since  the  volume  of  the  system 
was  known  for  each  pressure,  the  volume  of  nitrogen  adsorbed  on  the 
charcoal  could  be  easily  calculated.  The  nitrogen  could  be  completely 
pumped  off  at  25°.  A  typical  table  is  given  in  Table  2  as  an  example 
of  the  method  of  recording  results.  Fig.  4  represents  the  concentration 


pressure  curves  for  nitrogen  as  plotted  from  the  data  obtained  with  the 
various  charcoals. 

TABLE  II. 

Adsorption  of  Nitrogen  by  A9O9  Es.  3. 
Vol.  system. 


T. 

P. 

v~c. 

N.  T.  P. 

rress. 
Mm.  Hg. 

K0VOI 

temp. 

Bulb. 

Line.  Sys.  N.T.P.    char. 

<~c.  gas 
per  g. 

75-89 

ig.o 

760 

70 

99 

760.0 

10.66 

10.66 

60.33 

9.46 

32.38 

19  5 

760 

30 

.21 

235-8 

19.8 

3.32 

2.58 

5.90 

24-31 

3-84 

26.06 

19.5 

760 

24 

.33 

186.0 

19.8 

2.67 

1.83 

4-50 

19.82 

3.11 

20.38 

I9.5 

760 

19 

.01 

142.0 

20.  o 

i  99 

1.26 

3-25 

15.76 

2.48 

14-97 

19  5 

760 

13 

97 

IOI.5 

20.  o 

1.42 

0.80 

2.22 

"•75 

1.84 

II  .96 

19.7 

760 

II 

.16 

8o.O 

19  7 

I  .  12 

O.6o 

1.72 

9-44 

1.48 

8.62 

20.  o 

760 

g 

03 

48.9 

20.3 

O.69 

0.34 

1-03 

7-00 

I.  10 

4.66 

20.2 

760 

4 

-34 

21.7 

20.  6 

O.3O 

0.13 

0-43 

3  91 

0.61 

1.98 

20.2 

760 

i 

.84 

5-i 

20.3 

O.O7 

O.O3 

O.  IO 

1.74 

0.27 

o.  18 

20.3 

760 

0 

17 

0.2 

20.  6 

0.17 

0.03 

The  measurements  of  the  concentration  pressure  relation  with  carbon 

dioxide  were  made  in  exactly  the  same  way  as  those  with  the  nitrogen 

except  for  the  necessary  modifications  due  to  the  much  larger  amounts 

760 


o       4      8    12    16   20   24   28   32    36   40   44   48   52    56  60 

Cc.  CO-2  per  gram. 
5. — Adsorption  isotherms  for  carbon  dioxide  on  charcoals  at  25°. 


adsorbed.  This  necessitated  several  fillings  of  the  gasometer  R.  For 
the  admission  of  carbon  dioxide,  the  generator  was  sealed  to  the  apparatus 
shown  in  Fig.  3  at  H.  The  generator  was  furnished  with  a  mercury  valve 
immediately  before  a  stopcock  which  separated  it  from  the  rest  of  the 
system.  Carbon  dioxide  was  generated  and  allowed  to  escape  through 
this  valve  until  tests  showed  that  the  gas  was  completely  adsorbed  by  a 
caustic  potash  solution.  The  concentration  pressure  curves  obtained 
for  carbon  dioxide  on  the  different  charcoals  are  shown  in  Fig.  5.  It 
was  found  that  the  complete  removal  of  the  carbon  dioxide  from  the  char- 
coal at  the  temperature  of  adsorption  was  a  slow  and  tedious  process.  The 
gas  came  off  very  slowly  at  the  lowest  pressures,  as  much  as  8  cc.  per  g. 
of  charcoal  being  retained  by  one  of  the  charcoals  at  a  pressure  of  i  .4  mm. 
Hg.  The  only  exception  to  this  was  in  the  case  of  the  German  charcoal, 
with  which  the  amount  adsorbed  per  g.  was  about  half  that  of  the  amount 
adsorbed  by  the  other  charcoals,  and  where  the  carbon  dioxide  was  readily 
pumped  off  at  25°.  In  order,  therefore,  to  free  the  surface  from  adsorbed 
gas,  the  tube  was  immersed  in  a  tube  of  boiling  aniline  vapor.  It  was 
very  readily  possible  at  this  temperature,  184°,  to  recover  completely 
the  amount  of  carbon  dioxide  originally  admitted. 

Admission  of  Water. 

To  admit  water  to  the  charcoal,  the  apparatus  shown  in  Fig.  i  was 
sealed  to  the  stopcock  M,  Fig.  2,  in  place  of  the  apparatus  used  for  the 
admission  of  the  gases.  The  preparation  of  the  water  for  use  has  been 
described  previously.  After  the  last  freezing  in  the  preparation,  the 
ice  in  T  was  allowed  to  melt  and  a  beaker  of  warm  water  was  placed 
around  the  bulb  containing  the  water.  Since  the  apparatus  was  filled 
only  with  water  vapor,  the  water  distilled  and  filled  the  tube  S,  which  had 
been  calibrated  writh  a  thread  of  mercury  (0.123  cc.  per  cm.  tube)  com- 
pletely to  the  stopcock  M.  A  scale — one  division  =  0.581  mm.,  was 
fastened  to  the  tube  S  and  in  this  way  the  amounts  of  water  admitted 
to  the  charcoal  could  be  directly  read  to  0.007  cc-  and  estimated  one 
place  farther.  Since  the  adsorption  was  to  be  measured  at  25°,  which 
is  several  degrees  higher  than  ordinary  room  temperature,  means  had 
to  be  provided  to  prevent  distillation  from  the  charcoal  to  the  line  which 
was  in  the  air  above  the  thermostat.  At  first,  heating  by  means  of  a 
Nichrome  wire  wound  around  that  part  of  the  line  was  tried,  a  small  cur- 
rent, which  was  sufficient  to  keep  the  line  at  about  30°  as  determined  ex- 
perimentally, being  passed  through  the  wire.  Later  it  was  found  to  be 
more  convenient  to  raise  the  room  temperature  to  27-30°,  thereby  re- 
moving this  difficulty.  This  necessitated  the  cooling  of  the  thermostat 
by  means  of  ice.  It  was  customary  to  cool  the  bulb  to  10-15°,  causing 
more  rapid  distillation  from  the  line  to  the  charcoal,  and  then  allowing 
the  temperature  to  slowly  rise.  The  pressure  was  read  when  the  tern- 


perature  reached  25°.  As  this  pressure  approached  that  of  water  at 
2 5°>  23 -5  mm.,  it  was  sometimes  necessary  to  repeat  this  cooling  be- 
fore the  pressure  would  remain  constant.  It  frequently  required  3  to  5 


i 60      240 


640      720      800 


320       400       480       560 
Mg.  H2O  pe.r  gram. 
Fig.  6. — Adsorption  isotherms  for  water  vapor  on  charcoals  at  25°. 

hours  for  equilibrium  to  be  reached.  The  curves  of  concentration  pressure 
of  water  on  the  various  charcoals  are  shown  in  Fig.  6.  A  typical  table  of 
experimental  data  is  also  appended  in  Table  III : 


TABLE  III. 

Adsorption  of  Water  by  English  Charcoal  at  25°. 

c.  of  water 

Pressure 

Room 

Cc.  of  water 

Cc.  of  water 

G.  of  water 

G.  of  water  per 

0.0357 

10.2 

27.8 

0.00015 

0.0355 

0.0354 

0.0277 

0.0743 

12.  I 

2Q.2 

O.OOOI5 

0.0741 

0.0738 

0.0577 

0.1458 

13.8 

29.6 

O.OOOI7 

0.1456 

0.1449 

O.II33 

0.2886 

17.2 

30.4 

O.OOO26 

0.2883 

0.2872 

0.2247 

0.43H 

19.8 

29.4 

O.OOOJO 

0-43H 

0.4295 

0.3360 

0.5742 

21  .2 

29.6 

0.00032 

0-5739 

0.5720 

0-4473 

0.7184 

22.4 

'    30.2 

0.00034 

0.7181 

0.7156 

0-5595 

0.8262 

22.6 

30.3 

0.00034 

0.8259 

0.8230 

0.6441 

1.0047 

23-4 

29.9 

0.00036 

I  .0043 

1.0009 

0.7831 

Discussion. 

A  consideration  of  these  data  on  adsorption  shows  that  the  isotherms 
obtained  for  nitrogen  and  carbon  dioxide  on  the  various  charcoals  are 
of  the  same  general  form  as  previously  obtained  by  other  investigators, 


i.  e.,  Homfray,1  Titoff,2  Travers,3  Baerwald.4  Furthermore,  the  quanti- 
ties adsorbed  do  not  vary  much  among  themselves  for  equal  weights  of 
the  various  charcoals,  except  for  the  specially  treated  German  charcoal. 
A  slightly  larger  adsorptive  capacity  for  nitrogen  and  carbon  dioxide  was 
noticed  for  the  finely  divided  A9©9  than  for  the  large  grained  sample. 
This  is  taken  to  indicate  that  the  increase  in  surface  due  to  pulverizing 
the  charcoal  was  small,  less  than  8%,  in  comparison  with  the  total  avail- 
able surface  present  in  the  larger  grained  material. 

In  Table  IV  there  are  given  the  amounts  of  nitrogen  and  carbon  dioxide 
adsorbed  by  one  cc.  of  the  different  charcoals,  at  25°  and  760  mm.,  to- 
gether with  their  service  times.  It  is  necessary  to  use  equal  volumes 
of  the  charcoals  for  this  comparison  with  the  service  time,  as  this  latter 
test  is  made  on  a  constant  volume  of  charcoal.  This  can  be  obtained 
by  multiplying  the  volume  adsorbed  per  gram  charcoal  by  the  apparent 
density  of  the  charcoal.  It  is  very  readily  seen  from  this  table  that  there 
is  no  relation  between  the  capacity  for  a  charcoal  to  adsorb  a  gas,  as  nitro. 
gen  or  carbon  dioxide,  and  its  service  time. 

TABLE  IV. 

Cc.  N.  T.  P.  per  cc.  of  charcoal. 

• • >  Minutes 

N2.  COj.  service. 

A909 4-97  26.53  17-3 

Nela 4.89  25.04  53.5 

English 1.29  6.21  8.8 

German i.oi  7.35  60.2 

In  the  exponential  formula,  q  =  a.pl/n,  for  adsorption  isotherms,  Titoff5 
found  that  the  value  of  n  is  very  close  to  unity  for  gases  which  at  ordinary 
temperatures  may  be  called  "perfect  gases"  and  that  it  increases  in  value 
for  gases  of  increasingly  high  critical  temperatures.  This  would  give 
approximately  a  straight  line  to  the  isotherms  of  the  perfect  gases  and 
the  curves  would  become  more  and  more  concave  to  the  pressure  axis 
for  gases  with  increasingly  higher  critical  temperatures.  If  this  generality 
could  be  applied  even  to  cases  where  the  measurements  were  made  on  a 
vapor  which  could  exist  normally  as  a  liquid  under  the  conditions  of  the 
measurements,  as  water  in  our  experiments,  we  should  expect  that  the 
isotherm  for  water  would  be  very  much  more  concave  to  the  pressure 
axis  than  that  for  carbon  dioxide.  However,  the  curves  obtained  for 
water  are  of  a  form  exactly  opposite,  that  is,  they  are  concave  to  the  con- 
centration axis. 

Charcoal,  being  of  a  porous  nature,  besides  presenting  enormous  sur- 

1  Homfray,  Z.  physik.  Chem.,  74,  129  (1910). 

2  Titoff,  ibid.,  74,  641  (1910). 

*  Travers,  Proc.  Roy.  Soc.,  78,  9  (1907). 
4  Baerwald,  Ann.  Physik,  23,  90  (1907). 

*  Loc.  cit. 


13 

face  and  accordingly  having  high  adsorptive  capacity,  also  offers  the  op- 
portunity of  capillary  action,  especially  to  the  vapor  of  a  liquid  which  has 
as  high  a  surface  tension  as  water.  The  isotherms  for  water  must,  there- 
fore, be  taken  to  show  that  in  this  case  the  capillary  action  is  greater  than 
the  surface  attraction  of  adsorption,  since  they  are  just  what  would  be 
expected  from  the  assumption  that  water  was  taken  up  predominatingly 
by  capillary  action.  In  this  case,  the  smaller  capillaries  would  be  filled 
first  since  they  would  give  the  lower  vapor  pressures.  The  smaller  the 
diameter  of  the  capillaries,  the  more  rapidly  would  they  be  filled  by  a 
given  amount  of  water  and  so  the  pressure  would  increase  more  rapidly 
at  first  in  relation  to  the  concentration  than  when  the  capillaries  were  of 
a  larger  diameter.  This  would  satisfactorily  explain  the  concavity  to 
the  concentration  axis  obtained  for  the  isotherms  for  water. 

A  further  indication  that  water  vapor  is  not  adsorbed,  but  absorbed,  by 
charcoal  is  given  by  the  comparison  of  the  ratios  of  nitrogen,  carbon  di- 
oxide, and  water  taken  up  per  g.  of  the  various  charcoals.  These  ratios 
are  for  AQOQ,  Nela,  English  and  German  charcoals,  respectively,  i  .'5.3  : 
29.9;  i  :  5.0  :  54.2;  i  :  4.8  :  98.  i  ;  and  i  :  7.4  :  226.4.  It  is  seen  that 
while  there  is  more  or  less  regularity  between  the  ratios  of  nitrogen  and 
carbon  dioxide,  the  water  varies  between  the  wide  limits  of  29  .  9  and  226.4. 
This  must  surely  mean  that  if  charcoal  adsorbs  gases,  it  does  not  adsorb 
water  vapor,  but  that  this  is  a  different  phenomenon,  which  may  be 
called  absorption. 

A  quite  pronounced  break  can  be  seen  in  the  isotherms  for  water  on 
the  different  charcoals,  with  the  exception  of  the  finely  divided  A9O9. 
In  a  study  on  the  "adsorption"  of  water  by  silica  gel,  Anderson1  obtained 
a  similar  break.  He  seems  justified,  from  his  later  work  on  the  study  of 
the  velocity  of  adsorption,  to  conclude  that  this  break  marks  the  inter- 
section of  2  phenomena,  the  first  smooth  part  of  the  curve  represents 
the  taking  up  of  water  vapor  by  capillary  action,  the  break  occurs  only 
when  the  capillaries  have  filled  up  and  the  further  increase  in  vapor  pressure 
is  due  merely  to  the  flattening  of  the  meniscus  at  the  ends  of  the  capil- 
laries. 

Anderson  developed  in  his  paper  a  formula  which  can  be  used  for  the 
calculation  of  the  diameters  of  the  capillaries  from  the  vapor  pressure 
measurements.  By  means  of  this  formula,  it  is  also  possible  to  calculate 
the  surface  of  the  charcoal  since  the  volume  of  each  size  capillary  can  be 
obtained  directly  by  reference  to  the  concentration  axis.  The  formula  is 

2  r.50.  0.4343 


where  r  =  radius  of  the  capillary;  T  =  surface  tension  in  dynes  per  cm. 
1  Anderson,  Z.  physik.  Chem.,  88,  191  (1914). 


14 

at  25°  =  72 .  i ;  50  =  vapor  density  of  water  vapor  above  water  at  25°  = 
22.75  X  lo"6;  d  =  density  of  water  at  25°  =  0.99707;  p0  =  vapor 
pressure  in  dynes  of  water  at  25°  =  23.517  X  13.534  X  980.1  =  31.20  X 
io4;  and  pi  =  the  vapor  pressure  in  the  capillary. 

The  lowest  pressure  measured  in  our  experiments  was  2 . 3  mm.  on  the 
Nela  charcoal  when  16  mg.  of  water  had  been  absorbed  per  g.  of  charcoal. 
This  corresponds  to  a  capillary  diameter  of  9.1  X  io~8  cm.  A  vapor 
pressure  of  one  mm.  represents  a  pore  with  a  diameter  of  6.7  X  io~8 
cm.  In  Table  V  are  listed  the  smallest,  largest  and  mean  diameters  of 
the  capillaries  in  each  charcoal,  as  calculated  from  this  equation,  together 
with  the  surface  as  calculated  by  applying  this  formula  as  indicated  above . 


TABLE  V. 

Capillary  diameters. 

Cal.  surface. 

Smallest. 
Cm. 

.      6.7  X  10-8 
6  7  X  io 

Largest. 
Cm. 

4.1  X  lo-^ 
5-5  X  io 
1.9  X  io 

1.3    X    10 

Mean. 
Cm. 

2.8   X    10-' 
37   X    10 

8.3  X  io 
o.  s  X  io 

Per  g. 

230 
440 
300 
160 

Per  cc. 
M.    - 

130 
2OO 
40 
4.O 

Nela 

English  .... 
German  .  .  . 

..      1.6  X  io 

2.O   X    IO 

Lamb,  Wilson,  and  Chancy1  have  estimated  that  the  surface  of  one  g. 
of  an  activated  charcoal  is  about  1000  square  meters,  which  from  our 
data  would  appear  to  be  too  great.  Recently  A.  M.  Williams,2  in  de- 
veloping a  new  interpolation  formula  for  the  adsorption  of  gases,  was 
able  to  calculate  that  the  surface  of  the  charcoal  used  by  Dr.  Ida  F.  Horn- 
fray3  was  131  square  meters,  which  agrees  wrell  with  the  values  we  have 
obtained,  especially  when  one  considers  that  this  was  a  pre-war  product 
and  not  activated.  With  a  surface  of  the  magnitude  given  by  our  cal- 
culations, adsorption  of  nitrogen  and  carbon  dioxide  at  ordinary  tem- 
peratures and  to  pressures  as  high  as  atmospheric  could  well  be  in  a  mono- 
molecular  layer,  such  as  is  characterized  as  true  adsorption  by  Langmuir,4 
since  50  cc.  of  carbon  dioxide  at  N.  T.  P.  wrould  occupy  in  a  monomolec- 
ular  layer  a  surface  of  less  than  150  square  meters.  Also  the  fact  that, 
while  the  differences  in  the  calculated  surfaces  of  A9O9,  Nela,  and  English 
charcoals  is  considerable,  there  is  not  a  corresponding  difference  in  the  ad- 
sorption of  the  gases,  this  would  make  the  concept  of  "elementary  spaces" 
postulated  by  Langmuir3  necessary.  The  difference  in  the  adsorptive 
capacity  of  a  given  charcoal  for  nitrogen  and  carbon  dioxide  would  then 
depend  solely  on  the  difference  in  "time-lag"  of  the  condensation  evapora- 
tion process  of  adsorption. 

Since  it  has  been  shown  that  the  taking  up  of  water  vapor  is  a  different 

1  Lamb,  Wilson  and  Chancy,  J.  Ind.  Eng.  Ghent.,  u,  430  (1919). 

2  Williams,  Proc.  Roy.  Soc.,  g6A,  287  (1919). 
«  Loc.  cit. 

4  Langmuir,  J.  Am.  Client.  Soc.,  40,  1361  (1918). 


15 

phenomenon  from  adsorption,  it  is  interesting  to  see  whether  there  is  any  re- 
lation between  this  phenomenon,  absorption,  and  service  time.  The  neces- 
sary data  for  this  comparison  is  collected  in  Table  VI.  In  this  table  the 
per  cent,  weight  of  chloropicrin  held  by  the  charcoal  at  the  break  point, 
the  saturation  point,  and  the  "retentivity"  point  are  calculated  to  volume 
of  chloropicrin.  The  retentivity  signifies  the  amount  of  chloropicrin  left 
in  the  charcoal  on  reversing  the  test  until  no  trace  of  chloropicrin  can  be 
detected  in  the  effluent  air.  The  density  of  chloropicrin  at  25°  has  been 
taken  to  be  i .  65 1 ,  the  density  determined  at  the  American  University 
being  d?  =  1.6539. 

TABLE  VI. 

Vol.  chloropicrin  in  cc.  at.  Vol.  capillaries  per  g. 

Break.  Saturation.         Retentivity.  Total.        At  break  in  curve. 

Agog 0.0884  0.1762  0.0806  0.2728  0.1735 

Nela 0.2948  0.4406  0.3083 

English 0.1938  0.3967  0.0696  0.7828  0.6435 

German 0.6561  0.8174  0.1726  0.8543  0.4948 

Here,  also,  we  see  no  relation  between  service  time  and  capillary  action. 
Further,  there  does  not  appear  to  be  any  relation  between  the  volume 
of  the  capillaries  and  retentivity  or  saturation,  except  as  might  be  ex- 
pected the  saturation  occurs  in  each  case  before  the  capillaries  were  com- 
pletely filled,  due  to  the  fact  that  the  lower  layers  of  charcoal  had  not  yet 
reached  saturation. 

This  complete  lack  of  quantitative  relation  between  service  time  with 
the  phenomena  of  adsorption  and  absorption  is  not  startling.  The  test, 
as  developed,  was  only  empirical  and  such  factors  as  size  of  mesh  of  the 
sample  and  resistance  to  the  passage  of  air  were  known  to  have  a  marked 
influence  on  the  service  time.  It  is  this  "sieve  effect"  of  removing  the 
vapors  from  the  air  that  is  the  uncertain  and  indeterminate  factor  in  the 
minutes  service  that  a  charcoal  can  give.  We  know  of  no  other  phe- 
nomena, however,  which  can  explain  the  mechanism  of  this  removal  of 
gases,  or  vapors,  of  high  critical  temperature  from  those  of  much  lower, 
than  adsorption  and  absorption.  We  must  conclude,  therefore,  that 
both  of  these  phenomena  are  probably  involved  in  the  determination  of 
service  time,  and,  from  our  work  on  the  absorption  of  water  vapor,  that 
capillary  action  predominates  over  the  influence  of  unmodified  surface 
action  or  adsorption. 

Conclusions. 

1 .  No  relation  between  service  time  and  adsorption  of  a  gas,  as  nitrogen 
or  carbon  dioxide,  by  various  charcoals  has  been  found  to  exist. 

2.  Measurements  of  the  adsorption  of  these  gases  by  charcoals  have 
shown  that,  according  to  the  original  preparation  of  the  charcoal,  the  ad- 
sorptive  capacity  per  gram  of  charcoal  at  25°  and  760  mm.  may  vary  as 
much  as  100%. 


i6 

3.  It  has  been  shown  that  the  adsorption  of  nitrogen  and  carbon  di- 
oxide by  charcoal  may  be  considered  to  be  in  a  condensed  layer  one  mole- 
cule deep. 

4.  Measurements  of  the  isothermal  adsorption  of  water  vapor  by  char- 
coal at  25°  show  that  water  is  not  adsorbed  by  charcoal  but  is  held  by 
capillary  action,  i.  e.,  is  absorbed. 

5.  Using  Anderson's  formula  connecting  the  radius  of  a  capillary  with 
vapor  pressure,  the  mean  diameters  of  the  capillaries  of  the  4  charcoals 
used  have  been  calculated  and  have  been  found  to  vary  between  2 . 8  X 
io~7  cm.  and  9.2  X  io~7  cm.     The  maximum  diameter  in  any  of  the 
charcoals  was  determined  to  be  i  .3  X  io~6  cm. 

6.  By  means  of  this  same  formula  and  the  isothermals  for  water,  the 
surfaces  of  the  various  charcoals  were  found  to  vary  from  1 60  square  meters 
to  436  square  meters  per  gram  of  charcoal. 

7.  It  was  pointed  out  that  this  variation  in  surface  was  not  always  ac- 
companied by  a  corresponding  variation  in  adsorptive  capacity.     This 
makes  the  concept  of  "elementary  spaces"  as  postulated  by  Langimiir 
necessary. 

8.  No  relation  between  the  service  time  of  the  different  charcoals 
with  the  volume  of  the  capillaries  was  found.     The  same  was  true  for  the 
saturation  point  and  the  retentivity  of  these  charcoals.     This  lack  of  rela- 
tion must  indicate  that  other  indeterminate  factors  must  influence  largely 
the  minute  service  of  a  charcoal;  i.  e.,  the  2  phenomena,  adsorption  and 
capillary  action  are  insufficient  in  themselves  to  explain  this  test. 


STUDIES  IN  THE  ADSORPTION  BY  CHARCOAL. 
H.  RELATION  OF  OXYGEN  TO  CHARCOAL. 

De  Saussure,1  in  one  of  the  first  quantitative  measurements  of  adsorp- 
tion by  charcoal,  was  unable  to  obtain  results  for  oxygen  because  it  alone 
of  the  gases  would  not  apparently  come  to  equilibrium  even  after  a  year. 
This  anomalous  behavior  in  the  adsorption  of  oxygen  by  charcoal  has 
been  largely  overlooked  by  recent  investigators  though  previously  recog- 
nized and  recorded  by  R.  Angus  Smith,2  who  found  that  the  adsorption 
of  oxygen  continued  for  at  least  a  month,  though  this  was  not  true  for 
hydrogen,  nitrogen  or  carbon  dioxide;  and  that,  when  it  was  sought  to 
remove  the  oxygen  by  heat,  carbon  dioxide  was  given  off  in  place  of 

1  De  Saussure,  Gilb.  Ann.,  47,  113  (1814). 

*  R.  A.  Smith,  Proc.  Roy.  Soc.,  12,  424  (1863). 


oxygen,  by  H.  Kayser,1  who  found  that  the  adsorption  of  oxygen  had  not 
reached  an  end  after  two  weeks;  and  by  J.  Bohm,2  who  found  that  nitro- 
gen absorbed  by  charcoal  could  be  completely  removed  but  that  oxygen 
could  be  only  partly  removed  "even  by  boiling  water." 

However,  in  the  exhaustive  work  on  adsorption  by  Dr.  Ida  F.  Homfray,3 
as  in  that  of  Baerwald4  and  in  that  of  Lemon,5  no  such  peculiarities  in  the 
behavior  of  oxygen  were  noticed.  Dr.  Homfray  obtained  equilibrium 
with  the  various  gases  in  from  a  few  minutes  to  Vz  hour,  depending  on 
the  temperature,  and  so  apparently  missed  this  peculiar  effect  first  re- 
corded by  De  Saussure.  These  later  investigators  also  were  not  concerned 
with  the  recovery  of  the  adsorbed  gases  as  such,  so  they  did  not  observe 
the  second  peculiarity  mentioned  by  Smith,  i.  e.,  the  fact  that  the  oxygen 
may  be  recovered  only  partly  as  oxygen,  the  rest  being  recovered  only  as 
oxides  of  carbon. 

In  our  work  on  the  adsorptive  power  of  the  war  charcoals  we  noticed 
this  singular  difficulty  of  obtaining  equilibrium  with  oxygen.  Further- 
more, in  attempting  to  determine  the  moisture  and  gas  content  of  these 
charcoals,6  it  was  noticed  that  gases  continued  to  be  given  off  to  a  vacuum 
as  the  temperature  was  raised.  Up  to  900°,  these  gases  consisted  almost 
entirely  of  carbon  dioxide  and  carbon  monoxide,  the  first  predominating 
at  the  lower  temperatures  and  the  latter  at  the  higher.  At  about  1000°, 
carbon  dioxide  and  monoxide  practically  ceased  to  be  obtained.  Above 
1000°  hydrogen  began  to  be  more  noticeable  and  to  come  off  in  increasingly 
large  quantities  as  the  temperature  was  raised.  The  hydrogen  was  pre- 
sumably from  hydrocarbons  undecomposed  in  the  original  preparation 
of  the  charcoals. 

When  a  charcoal  has  been  thoroughly  "outgassed"  at  900°  to  1000° 
and  allowed  to  cool  to  room  temperature  in  a  vacuum  and  gases  admitted, 
it  was  found  possible  to  recover  completely  such  gases  as  hydrogen, 
nitrogen,  and  carbon  monoxide  at  room  temperature,  though  the  rate  at 
which  they  could  be  collected  in  a  Topler  pump  was  increased  by  raising 
the  temperature;  90%  of  the  carbon  dioxide  could  be  recovered,  and 
smaller  percentage  of  the  water,  at  room  temperature,  but  both  could  be 
quantitatively  obtained  at  184°  (aniline  b.  p.)  as  rapidly  as  possible  to 
collect  them  with  a  Topler  pump  for  the  carbon  dioxide  and  with  a  con- 
denser cooled  with  solid  carbon  dioxide  for  the  water. 

However,  when  oxygen  was  admitted  and  allowed  approximately  to 
come  to  equilibrium,  only  about  half  was  recovered  by  evacuating  at 

H.  Kayser,  Wied.  Ann.,  12,  526  (1881). 

J.  Bohm,  Bot.  Z.,  1883,  32-34. 

F.  Homfray,  Z.  physik.  Chem.,  74,  129  (1910). 

Baerwald,  Ann.  Physik,  23,  90  (1907). 

Lemon,  Phy.  Rev.,  [2]  14,  281,  394  (1919)- 

C.  W.  S.  Reports,  Sept.-Dec.,  1918. 


i8 

room  temperature  and  only  traces  on  increasing  the  temperature  to  184°, 
though  on  again  cooling  to  room  temperature  and  again  admitting  oxygen, 
this  second  lot  was  readily  recovered.  Therefore  attempts  were  made 
to  recover  completely  this  oxygen,  which  had  apparently  disappeared, 
by  increasing  the  temperature  still  further,  and  soon  carbon  dioxide  and 
monoxide  began  to  appear,  but  not  until  a  temperature  of  900°  to  1000° 
was  again  reached  was  all  the  oxygen  recovered  and  then  not  as  oxygen 
but  as  these  oxides  of  carbon.  We  have  interpreted  this  to  indicate  that 
there  were  here  2  phenomena,  adsorption  and  "fixation"  or  "combina- 
tion" of  the  oxygen  with  the  charcoal.  The  adsorbed  oxygen  was  re- 
garded as  that  which  was  recoverable  by  evacuating  at  room  tempera- 
ture, and  the  "fixed"  oxygen  that  which  was  recovered  only  as  the  oxides 
of  carbon  at  higher  temperatures. 

These  facts  led  us  to  a  more  thorough  investigation  of  this  fixation  of 
oxygen  by  charcoal,  both  as  to  the  length  of  time  necessary  to  reach  satura- 
tion and  also  as  to  the  amounts  of  oxygen  which  could  be  held  in  this 
way  by  the  charcoal.  For  this  purpose  we  used  3  samples  of  war  charcoal 
described  in  the  preceding  paper  as  Agog,  English,  and  German.  Their 
moisture  and  adsorbed  gas  contents  were  known,  and  the  samples  were 
kept  in  carefully  stoppered  bottles. 

Experimental. 

A.  Determination  of  Equilibrium  of  Charcoal  and  Oxygen  at  250  and 
760  mm. — For  this  purpose,  3  bulbs  of  about  25  cc.  capacity  each  were 
filled  with  the  above  named  charcoals  and  each  was  sealed  to  a  line  which 
led  either  to  a  Topler  pump  or  to  a  buret  containing  pure  electrolytic 
oxygen.  Each  bulb  was  separated  individually  from  the  line  by  a  one- 
way stopcock,  and  during  the  measurements  was  kept  immersed  in  a 
thermostat  at  25°  ±  o.  i°.  As  a  preliminary  treatment,  the  samples 
were  thoroughly  freed  from  adsorbed  gases  by  outgassing  at  184°,  leav- 
ing in  them,  however,  the  fixed  oxygen  they  originally  contained.  When 
the  bulbs  had  been  cooled  in  the  thermostat,  oxygen  was  admitted  at 
760  mm.  by  a  constant  pressure  arrangement.  From  the  temperature 
of  the  buret,  the  amount  of  oxygen  admitted  to  the  bulb  was  reduced 
directly  to  N.  T.  P.  After  the  first  correction  for  the  dead  space  in  the 
bulb,  the  amount  taken  up  each  time  was  divided  by  the  weight  of  the 
moisture  and  gas-free  sample,  reducing  the  results  to  cc.  of  oxygen  per  g. 
of  sample. 

Fresh  oxygen  was  admitted  from  time  to  time  and  the  amounts  re- 
corded. At  the  end  of  the  first  100  hours,  when  the  amounts  of  oxygen 
taken  up  at  successive  intervals  were  becoming  less,  each  sample  was 
evacuated  thoroughly  at  25°.  In  no  case  was  the  amount  of  oxygen 
originally  admitted  recovered.  In  some  cases  traces  of  carbon  dioxide 
and  carbon  monoxide  were  found  in  the  gases  collected.  Since  the  sam- 


pies  were  largely  oxygen,  it  was  thought  possible  that  the  small  amounts 
of  carbon  monoxide  were  from  the  alkaline  pyrogallate  used  to  absorb 
the  oxygen.  Oxygen  was  then  admitted  and  its  course  followed.  This 
was  repeated  until  equilibrium  was  reached.  This  was  most  quickly 
reached  by  the  English  charcoal  at  the  end  of  1600  hours  or  66  days, 
while  the  German  charcoal  took  just  about  twice  this  length  of  time. 
The  data  is  presented  in  the  form  of  curves  as  shown  in  Figs,  i,  2  and  3. 


: 


A909 


O  150300    60O     90O     1200    I5OO    I80O    2IOO    24OO    27OO  30OO 

Time  in  hours. 
Fig.  i. — Adsorption  and  fixation  of  oxygen  at  25°  and  760  mm.  by  Agog  charcoal. 

It  will  be  noticed  that  we  really  have  2  curves  from  each  series  of  mea- 
surements. The  upper  curve  represents  in  each  case  the  total  amount  of 
oxygen  taken  up  at  25°  and  760  mm.,  while  the  lower  dotted  curve  repre- 
sents that  which  cannot  be  obtained  by  evacuation  at  25°.  It  is  also 
apparent  that  the  slopes  of  the  2  curves  are  very  similar.  From  our 
previous  experience,  we  are  led  to  the  conclusion  that  the  lower  curve 
represents  the  rate  of  saturation  of  the  charcoal  by  what  we  have  called 
"fixed"  oxygen,  and  that  the  upper  curve  is  the  sum  of  2  effects,  true  ad- 
sorption and  fixation.  Since  this  is  the  case,  it  can  readily  be  seen  that 
the  long  time  necessary  to  reach  equilibrium  is  due  to  this  fixation  and 
that  the  true  adsorption  of  oxygen  by  charcoal  occurs  as  rapidly  as  for 
other  gases. 

These  measurements  have,  therefore,  shown  not  only  that  the  equi- 
librium between  oxygen  and  charcoal  is  attained  only  after  months  of 


9 

!; 


ENGLISH 


100  200300 


500 


1500 


1800 


8OO  IOOO         I2OO 

Time  in  hours. 
Fig.  2. — Adsorption  and  fixation  of  oxygen  at  25°  and  700  mm.  by  English  charcoal. 


contact,  but  also  that  the  cause  of  this  is  the  presence  of  2  effects,  true 
adsorption  and  "fixation." 


GERMAN 


«*?***" 


200  4°°  looo  2000  3000  4000 

Time  in  hours. 
Fig.  3. — Adsorption  and  fixation  of  oxygen  at  25°  and  760  mm.  by  German  charcoal. 


B.  Determination  of  Total  "Fixed"  Oxygen. — In  order  to  obtain  all 
the  fixed  oxygen  from  charcoal,  it  seemed  necessary  only  to  heat  the  sam- 
ple in  a  vacuum,  after  first  removing  all  the  adsorbed  gases  and  vapors, 
and  to  collect  and  analyze  the  evolved  gases.  The  carbon  dioxide  and 
monoxide  are  calculated  to  cc.  of  oxygen,  N.  T.  P.,  per  g.  of  charcoal.  The 


procedure  first  adopted  was  as  follows:  the  charcoal  was  heated  in  a  fused 
quartz  tube  in  an  aniline  bath  and  thoroughly  outgassed,  then  in  a  Ni- 
chrome  resistance  furnace  to  1050°.  Gases  continued  to  be  slowly  given 
off  for  several  hours  at  this  temperature  and  still  contained  small  per- 
centages of  the  oxides  of  carbon. 
Since  even  at  this  temperature 
the  charcoal  acted  on  the  fused 
quartz,  we  suspected  that  we 
were  not  getting  the  true  oxygen 
content  of  the  charcoal.  We 
observed  that  the  inner  surface 
of  the  tube  was  markedly  etched 
and  suspected  the  reduction  of 
the  silica  to  a  sub-oxide  so  that 
some  of  the  oxides  of  carbon 
might  well  have  been  from  this 
reduction.  In  view  of  this  situa- 


Fig.  4. 


tion,  it  seemed  necessary  to  devise  a  method  which  would  obviate  these 
difficulties  and  allow  us  to  go  to  still  higher  temperatures. 

The  development  of  the  high  frequency  induction  furnace  by  E-  F. 
Northrup1  seemed  to  offer  a  means  of  solving  our  difficulties.  The  com- 
pactness of  the  apparatus  afforded  by  this  method  of  heating  was  recog- 
j]  nized  to  be  one  of  its  many  advantages  over  other  forms 
of  electrical  heating.  Using  this  method  of  heating,  we 
have  found  it  possible  to  heat  charcoal  in  a  platinum 
cup  supported  in  a  quartz  vacuum  tube,  keeping  the 
quartz  at  a  low  temperature  even  when  the  cup  and 
charcoal  were  at  1400°.  In  this  way  the  possibility  of  a 
leak  through  hot  quartz  and  reduction  of  the  silica  to  a 
sub-oxide  were  prevented. 

The  apparatus  designed  for  this  experimental  work  is 
shown  in  Fig.  5.  It  consists  primarily  of  a  fused  quartz 
tube,  T,  25  cm.  long  and  2 . 5  cm.  outside  diameter,  with 
a  side  tube,  S,  connected  to  a  glass  tube  by  a 
de  Khotinsky  joint  leading  to  a  Topler  pump  through  a 
phosphorus  pentoxide  tube,  P.  The  upper  end  of  the 
quartz  tube  was  closed  by  an  optically  clear  piece  of  fused 
quartz ;  and  the  lower  end  by  a  stopper  of  Pyrex  glass  with 
a  ground  joint,  which  also  served  indirectly  as  a  support 


Fig.  5- 


for  a  platinum-rhodium  crucible,  X.     The  crucible  was  3.5  cm.  long  and 
1.5  cm.  in  diameter  and  had  a  platinum  pin  riveted  to  the  bottom.     This 
pin  fitted  in  a  fine  porcelain  tube,  C,  which  in  turn  was  held  in  the  Pyrex 
1  Northrup,  Trans.  Am.  Electrochem .  Soc.,  35,  69  (1919). 


support,.  In  order  to  prevent  radiation  downwards,  a  porcelain  disk,  R, 
was  fastened  to  the  small  porcelain  tube.  The  crucible  served  as  the 
resistor  and  was  rapidly  heated  by  the  induced  currents  from  the  primary. 
When  the  charcoal  was  heated  it  also  became  a  conductor  and  so  could 
be  directly  heated  by  the  induced  currents.  The  primary  was  a  coil  of 
flat,  copper  tubing  (Fig.  4),  the  inside  diameter  of  which  was  3.6  cm.  and 
the  height  15  cm.  The  coil  was  kept  cool  by  passing  a  stream  of  cold 
water  through  the  tubing,  and  the  proximity  of  this  coil  to  the  walls  of 
the  quartz  vacuum  tube  kept  the  quartz  at  a  low  temperature  in  spite 
of  the  radiation  from  the  platintim  crucible. 

For  measuring  the  temperature  of  the  charcoal,  a  Leeds  and  Northrup 
optical  pyrometer  of  the  Morse  type  was  used.  This  was  calibrated 
against  a  standard  thermocouple  between  800°  and  1400°.  Since  the  tem- 
peratures were  to  be  measured  optically,  black  body  conditions  had  to 
be  obtained.  This  was  done,  as  is  shown  in  the  cut,  by  placing  a  very 
thin,  platinum  truncated  cone  over  the  top  of  the  crucible  to  minimize 
the  radiation  from  the  surface;  and  then  a  platinum  tube  of  very  thin 
foil  of  o .  4  cm.  diameter  was  placed  in  the  center  of  the  sample  and  focusing 
was  made  on  the  surface  of  the  charcoal  at  the  bottom  of  this  tube. 

The  procedure  in  making  a  determination  was  as  follows :  The  crucible 
was  filled  with  a  known  weight  of  charcoal  and  the  apparatus  assembled 
as  described.  The  heater  shown  in  Fig.  6,  con- 
taining naphthalene  (b.  p.  218°),  was  placed 
around  the  quartz  tube  and  the  lower  end  stop- 
pered  and  covered  with  mercury.  The  naph- 
thalene was  then  brought  to  boiling  and  the 
vapors  allowed  to  condense  to  C  above  the  posi- 
tion of  the  platinum  crucible.  During  the  heat- 
ing the  charcoal  was  continually  outgassed  by 
means  of  the  Topler  pump  and  this  gas,  being 
regarded  as  adsorbed  gas,  discarded.  Then  the 
naphthalene  bath  was  replaced  by  the  primary 
coil  of  the  induction  furnace  and  the  charcoal 
heated  rapidly.  All  the  gas  was  collected  by 
the  Topler  pump  and  was  stored  in  a  large  gas  buret  over  mercury  and  a 
sample  of  this  analyzed. 

A  preliminary  run  was  made  on  the  Agog  in  order  to  determine  at  what 
temperature  the  oxides  of  carbon  ceased  to  be  obtained.  The  results  of 
this  experiment  are  shown  in  Table  I. 

They  show  that  the  amounts  of  oxygen  remaining  combined  with  the 
charcoal  above  1180°  are  extremely  small  and  could  be  neglected.  It 
seemed  important  to  see  what  gases  could  be  obtained  at  still  higher  tem- 
peratures, however,  and  so  in  2  of  the  experiments  the  temperature  was 


Fig.  6. 


23 

raised  to  1400°.  The  gas  at  these  high  temperatures  was  more  than 
99%  hydrogen  and  was  slowly  decreasing  in  amounts  obtained  as  the  tem- 
perature was  raised. 

TABLE    I. 


T 

Time  of 

Cc.  per  g. 

Fixed 

Cc.  per  g'. 

Temp,  limits. 

heating. 

CO2. 

CO. 

Hi. 

CH«. 

oxygen. 
Cc.  per  g. 

I... 

•       36 

•42 

200-1000° 

2       hrs. 

4 

66 

23.40 

8.32 

0.04 

16.36 

II... 

•       17 

.60 

IOOO-Il8o° 

aVshrs. 

o 

.08 

0.53 

16.93 

0.06 

0-35 

III... 

4 

.87 

Il8o-I26o0 

iVi-hrs. 

O 

.00 

0.07 

4.76 

0.04 

0.03 

Since  the  object  of  this  part  of  the  work  was  to  obtain  quantitatively 
the  amount  of  oxygen  capable  of  being  fixed  by  charcoals,  after  standard- 
ization of  the  method  with  ordinary  Agoy,  the  determinations  were  made 
on  the  3  samples  which  had  been  saturated  in  pure  electrolytic  oxygen. 
The  results  obtained  are  presented  in  Table  II.  In  this  table  are  first 
given  the  results  from  2  successive  runs  on  two  samples  of  A9OQ  in  order 
to  get  some  idea  as  to  the  reproducibility  of  the  results.  Considering  that 
charcoal  is  not  a  pure  substance,  the  agreement  is  regarded  as  very  good 


A909  (i) 
AQOQ  (2) 
(02  sat.) 
Agog 
English 
German 

Total  gas. 
Cc.  per  g. 

(N.  T.  P.) 

54  99 
58.89 

56.90 
43-79 

2OI  .OO 

Maximum 
temp. 

1100°  =*=  50 

1260° 

1226° 
1412° 
1412° 

TA 

Time  of 
heating. 

21/2  hrs. 

53/4  hrs. 

3      hrs. 
2l/4  hrs. 
3:/4  hrs. 

BLE    II. 

Cc.  N.  T. 

P.  per  g. 

Fixed  Oj  per 

K 

C02. 
5    19 

4-74 

5.76 
2.76 
9.76 

CO. 

22.  II 
24.00 

24.80 
18.36 
32.92 

H2. 
27-57 
30.01 

26.  19 
22.56 
154-5 

CH«.  Cc 
O.  12 
0.14 

0.15 
O.  II 
3-79 

.N.T.  P. 
16.25 
16.74 

18.16 
11.94 
26.25 

Wt. 
2 

2 

2 
I 

3 

%. 

32 
39 

59 
71 

75 

The  data  in  this  table  show  that  the  larger  part  of  the  oxygen  held  by 
the  charcoal  had  been  fixed  before  the  samples  had  been  "soaked"  in 
pure  oxygen.  A  comparison  of  the  amounts  of  oxygen  which  is  fixed  by 
the  different  charcoals  with  the  amounts  adsorbed  is  given  in  Table  III, 
together  with  the  ratio  of  fixed  to  adsorbed  oxygen.  This  shows  that  as 
much  as  6  times  the  amount  of  oxygen  adsorbed  by  a  charcoal  may  be 
held  as  "fixed"  oxygen. 

TABLE  III. 

Cc.  N   T.  P.  oxygen  per  g.  of  charcoal. 

• Ratio  of  fixed 

Fixed.  Adsorbed.  to  adsorbed  Oa. 

Agog 18.16  7.2  2.5 

English ii.  94  8.6  1.4 

German 26.25  4  •  2  6.3 

In  Table  IV  are  given  the  actual  observations  on  a  run,  in  order  to  give 
an  idea  of  how  an  experiment  proceeded,  after  the  sample  had  been  thor- 
oughly outgassed  at  200°. 


24 

TABLE  IV. 

Sample  Used — Agog  =  2.948  g. 


ime. 

Cc.  gas. 

Temp. 

T 

me.      C< 

.  gas. 

Temp. 

:  05 

O.OO 

25° 

:  15 

97-4 

959 

3 

45 

-5 

1190° 

:  25 

19.0 

1045 

3 

55 

-7 

1226 

:  35 

13-0 

1091 

4 

05 

.2 

1208 

:  45 

17.0 

1160 

4 

15 

.10° 

1196 

:  55 

10.5 

1178 

4 

25 

.06 

I2II 

3  :  05 

IO.O 

1172 

4 

35     C 

).90 

I2II 

3  :  15 

6.0 

1181 

4 

45     < 

)-72 

1205 

3  :  25 

4.0 

1196 

4 

55     c 

).6i 

12.11 

3  :  35 

2.7 

1166 

5 

05     c 

>.46 

1208 

0  These  small  volumes  were  measured  in  the  fall  tube  of  the  Topler  pump  (J. 
Ind.  Eng.  Chem.,  12,  40  (1920)). 

At  the  end  of  each  determination,  the  walls  of  the  quartz  tube  held  on 
their  inner  surface  a  thin  film  of  a  solid  varying  in  color  from  white  to 
brown,  which  had  vaporized  from  the  charcoal  at  the  high  temperatures. 
A  similar  observation  has  been  recorded  by  A.  Schuller,1  who  concluded 
that  this  was  organic  matter.  On  attempting  to  remove  this  film,  how- 
ever, the  odor  of  acetylene  was  noticed.  This  suggested  that  a  carbide 
had  been  formed  during  the  determination  and  that  accordingly  some  of 
the  oxides  of  carbon  obtained  might  well  have  been  from  reduction  of  min- 
eral matter  contained  in  the  ash.  In  order  to  determine  what  might  be 
the  magnitude  of  this  effect  on  the  data  obtained,  the  percentage  of  ash 
was  determined  for  each  charcoal  and  the  ash  analyzed.  In  the  AQOQ 
and  English  charcoals  this  was  mostly  alkali  carbonates  with  slight  traces 
of  alkaline  earths,  iron,  and  alumina.  In  the  German  charcoal  the  ash 
was  principally  iron  with  some  alkali  carbonates.  Table  V  presents  this 

TABLE  V. 

Calc.  cc.  Oi  per  Cc.  O->  remaining 

%  ash.  g.  of  charcoal.         "fixed"  by  charcoal. 

Agog i. ii  3.00  15.16 

English 2  . 04  5.41  6.53 

German 1.91  4-35  21.90 

data  and  the  maximum  amount  of  oxygen  which  could  under  any  circum- 
stances be  attributed  to  the  ash.  It  is  thought,  however,  that  the  amount 
of  reduction  at  these  comparatively  low  temperatures  was  in  all  cases 
much  less  than  these  figures  would  indicate.  In  any  case,  as  shown  in 
this  table,  the  ash  can  account  for  only  a  small  part  of  the  oxygen 
obtained  in  the  experiments  as  oxides  of  carbon. 

Discussion. 

Since  it  has  been  definitely  shown  that  oxygen  can  be  "fixed"  by  char- 
coal, other  than  by  adsorption,  it  becomes  an  interesting  problem  to  con- 
sider the  origin  and  state  of  this  oxygen.  The  original  material  from  which 

1  vSchuller,  Wied.  Ann.,  18,  317  (1883). 


25 

all  these  charcoals  were  prepared  was  organic  matter  and  as  such  con- 
tained in  the  molecular  complexes  both  oxygen  and  hydrogen.  It  seemed 
possible  that  both  the  oxygen  and  hydrogen  obtained  by  us  were  from 
some  of  the  original  material  which  had  not  been  decomposed  in  the 
preparation  of  the  charcoals,  but  against  this  view  we  find  the  following 
facts.  The  temperature  of  charring  this  original  material  was  in  all  cases 
very  close  to  the  temperature,  above  which  no  oxides  of  carbon  were  ob- 
tained and  only  above  which  hydrogen  and  methane  were  obtained.  This 
would  lead  us  to  the  conclusion  that  the  hydrogen  alone  was  from  the 
original  undecomposed  organic  material.  This  conclusion  is  supported 
by  the  fact,  which  was  pointed  out  in  the  introduction,  that  the  oxygen 
obtained  as  oxides  of  carbon  on  heating  in  a  vacuum  was  reversible  while 
the  hydrogen  was  irreversible.  An  actual  experiment  showed  that  90% 
of  the  oxygen  obtained  as  oxides  of  carbon  above  184°  was  fixed  by  the 
charcoal  a  second  time  in  99  hours.  On  the  other  hand,  in  every  case 
hydrogen  admitted  to  a  charcoal  after  outgassing  at  1050°  and  cooling 
to  room  temperature  could  be  readily  and  quantitatively  recovered  at 
room  temperature. 

In  view  of  these  facts,  we  have  concluded  that  this  fixed  oxygen  is  held 
by  the  charcoal  as  a  surface  compound  or  compounds.  These  com- 
pounds would  be,  therefore,  solid  oxides  of  carbon  high  in  carbon  and  low 
in  oxygen  content,  but  not  necessarily  in  which  the  ratio  of  carbon  to 
oxygen  was  constant.  These  oxides  must  be  stable  at  ordinary  tempera- 
tures, or  at  least  have  a  very  low  rate  of  decomposition,  the  decomposi- 
tion not  taking  place  appreciably  until  a  temperature  of  about  200°  is 
reached.  The  data  shows  that  these  oxides  then  break  down  slowly, 
giving  carbon  dioxide  and  carbon  monoxide  and  presumably  leaving  a 
residue  of  carbon.  Although  the  carbon  dioxide  predominates  at  the 
lower  temperatures  in  the  decomposition  and  carbon  monoxide  at  the 
higher,  no  conclusions  as  to  the  mechanism  of  the  original  decomposition 
can  be  made,  since  carbon  dioxide  liberated  in  immediate  contact  with 
carbon  at  the  higher  temperatures  would  react  immediately  with  the 
carbon  and  be  reduced  to  the  monoxide,  i.  e.,  there  would  be  a  tendency 
to  attain  equilibrium  between  carbon,  carbon  monoxide  and  carbon 
dioxide  at  any  given  temperature. 

This  conception  of  a  solid  oxide  of  carbon,  stable  at  ordinary  tempera- 
tures, is  not  new.  Brodie1  isolated  2  oxides  of  carbon  which  were  amorph- 
ous, brown  and  transparent  solids  to  which  he  assigned  the  formulas 
0564  and  CtO3t  and  indicated  that  he  considered  that  they  belonged  to  a 
series  of  oxides  corresponding  to  the  hydrocarbons  of  the  acetylene  series. 
Berthelot2  showed  that  these  oxides  decomposed  on  heating  to  300°  in  an 

1  Brodie,  Ann.,  169,  270  (1873). 

2  Berthelot,  Bull.  soc.  chim.,  26,  102  (1876). 


26 

atmosphere  of  nitrogen  to  an  oxide  still  higher  in  carbon  content  by  loss 
of  equal  volumes  of  carbon  dioxide  and  carbon  monoxide  and  to  which  he 
assigned  the  formula  CisOe-  Mellitic  anhydride,  C^Og,  has  recently  been 
prepared  and  its  properties  described  in  2  independent  investigations.1 
The  most  recent  work  on  graphitic  acid2  and  work  done  in  this  labora- 
tory (which  has  not  yet  been  published)  indicates  that  this  is  a  colloidal 
oxide  of  carbon  with  an  empirical  formula  approaching  C3O. 

Furthermore,  H.  E.  Armstrong,3  in  his  studies  on  the  combustion  of 
carbon,  concluded  that  the  simple  oxides,  carbon  dioxide  and  carbon  mon- 
oxide, were  obtained  only  by  the  breakdown  of  the  more  or  less  completely 
oxidized  carbon  complex.  The  later  extensive  researches  of  Rhead  and 
Wheeler*  on  the  same  subject  lead  to  the  conclusion  that  oxygen  com- 
bines with  a  mass  of  carbon  directly  to  form  a  "physico-chemical"  complex 
CxOy  of  variable  composition,  which  is  decomposed  by  heat  into  carbon 
monoxide  and  dioxide.  These  investigators  performed  some  interesting 
experiments  to  determine  the  amount  of  this  solid  carbon -oxygen  complex 
present  at  temperatures  from  100°  to  900°  during  the  combustion  of  car- 
bon. Their  results  indicate  that  the  higher  the  temperature,  the  less 
the  amount  of  the  complex  present.  If  we  extrapolate  their  results,  it 
would  appear  that  at  room  temperature  practically  no  carbon  monoxide 
or  dioxide  would  be  formed  but  only  the  complex,  while  above  about  1200° 
very  little  of  the  complex  would  be  formed.  This  agrees  entirely  with 
our  observations,  which,  interpreted  by  means  of  assuming  the  formation 
of  this  CjOy  complex,  shows  that  the  first  stage  in  the  combustion  of 
carbon  takes  place  at  ordinary  temperatures.  Langmuir5  has  shown 
that  a  similar  complex  of  carbon  and  oxygen,  presumably  an  extremely 
stable  solid  oxide  of  carbon,  was  formed  by  a  highly  graphitized  filament 
of  very  pure  carbon.  This  decomposed  only  slowly  at  1425°  but  readily 
at  1925  °  and  seems  to  have  been  even  more  stable  than  the  complex  formed 
by  oxygen  with  amorphous  carbon.  These  facts  all  indicate  that  oxygen 
does  combine  with  carbon  to  form  a  complex,  C^O^,  high  in  carbon  and 
low  in  oxygen  content,  which  decomposes  on  heating  to  give  the  ordinary 
oxides  of  carbon. 

We  are  led  further  to  the  conclusion  that  this  complex  must  be  formed 
on  the  surface  of  the  charcoal.  This  would  therefore  be  likely  to  alter 
the  adsorptive  capacity  of  a  charcoal,  which  would  thus  depend  in  part 
on  the  amount  of  this  complex  on  the  surface,  No  conclusive  data  on 
this  point  have  been  collected,  however,  since,  although  it  was  observed 

1  Meyer  and  Steiner,  Ber.,  46,  813  (1913);  and  Jarrad,  /.  Chem.  Soc.,  29,  106  (1913). 

2  Kohlschutter  and  Haenni,  Z.  anorg.  Chem.,  105,  121  (1919). 
1  Armstrong,  /.  Soc.  Chem.  2nd.,  24,  473  (1905). 

4  Rhead  and  Wheeler,  J.  Chem.  Soc.,  101,  831  (1912  •;  and  103,  461  (1912). 
6  Langmuir,  /.  Am.  Chem.  Soc.,  27,  1154  (1915). 


27 

•that  the  adsorptive  power  of  the  German  charcoal  with  the  most  fixed 
oxygen  was  the  lowest  and  the  English  charcoal  with  the  least  fixed  oxy- 
!gen  the  highest,  the  presence  of  undecomposed  hydrocarbons  was  also 
^greatest  in  the  German  and  least  in  the  English  charcoal.  So,  since  in 
;the  preliminary  treatment  of  the  charcoals  (Part  I),  most  of  the  fixed 
oxygen  was  removed  while  the  hydrocarbon  content  was  not  much  altered, 
the  differences  observed  are  more  likely  due  to  this  latter  cause. 

Conclusions. 

1.  The  anomalous  behavior  of  the  adsorption  of  oxygen  by  charcoal 
extending  over  long  periods  of  time,  overlooked  by  recent  investigators, 
has  been  confirmed.     This  is  shown  to  be  due  to  the  presence  of  2  phe- 
nomena, adsorption  and  surface  combination. 

2.  A  method  has  been  developed  for  heating  charcoal  in  a  vacuum  out 
!  of  contact  of  oxygen-containing  materials,  as  quartz,  to  high  tempera- 
i  tures  by  use  of  the  Northrup  induction  furnace.     The  gases  evolved 
'  were  collected  and  analyzed. 

j      3.  The  formation  of  a  carbon-oxygen   complex,   essentially  a  stable 

solid  oxide  of  carbon,  has  been  shown  to  occur  on  the  surface  of  charcoal 
1  at   ordinary   temperatures.     This   complex   decomposes   on   heating    to 

carbon  dioxide  and  carbon  monoxide  and  can  thus  be  considered  to  be 
-an  intermediate  step  in  the  combustion  of  charcoal,  which  supports  the 

view  suggested  by  Armstrong  and  supported  with  experimental  evidence 
<by  Rhead  and  Wheeler  and  by  Langmuir. 

4.  The  amounts  of  oxygen  thus  combined  to  the  charcoal  has  been 
und  to  vary  with  2  ; 

weight  of  the  charcoal. 


ACKNOWLEDGMENT 

My  sincere  thanks  are  due  to  Professor  G.  A.  Hulett  for  suggesting  this 
research,  and  for  the  very  valuable  advice  offered  during  the  progress  of 
the  work. 


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